gh-141172: Update to wasi-sdk-29 (GH-141684)

This commit updates CI and configuration from wasi-sdk-25 to wasi-sdk-29
which was released recently. This notably includes stubs for pthreads
which all return errors, so some adjustment in logic is necessary to
retain knowledge that WASI cannot yet spawn threads for example.

This additionally increases the wasm stack allowance to 32MiB from 16MiB
to accomodate the `test_recursive_pickle` test in the
`test_functools.py` file. It looks like the Clang/LLVM update that
happened in wasi-sdk-29 relative to wasi-sdk-25 is likely the cause of
this where presumably functions have more locals than before and/or a
slightly adjusted stack space requirement which overflows the stack.

Include/pyport.h

@@ -504,6 +504,7 @@ extern "C" {
  * Thread support is stubbed and any attempt to create a new thread fails.
  */
 #if (!defined(HAVE_PTHREAD_STUBS) && \
+     !defined(__wasi__) && \
       (!defined(__EMSCRIPTEN__) || defined(__EMSCRIPTEN_PTHREADS__)))
 #  define Py_CAN_START_THREADS 1
 #endif